The invention is based on a fuel injection method for an internal combustion engine and to a fuel injection system as generically defined by hereinafter.
One such injection system has been disclosed by European Patent Disclosure EP 0 711 914 A1, for instance.
For the sake of better comprehension of the ensuing description, several terms will first be defined further: In a pressure-controlled fuel injection system, by means of the fuel pressure prevailing in the nozzle chamber of an injector, a valve body (such as a nozzle needle) is opened counter to the action of a closing force, and the injection opening is thus opened for an injection of the fuel. The pressure at which fuel emerges from the nozzle chamber into the cylinder is called the injection pressure. Within the scope of the invention, the term stroke-controlled fuel injection system is understood to mean that the opening and closure of the injection opening of an injector are accomplished with the aid of a displaceable valve member on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. Furthermore, an arrangement will hereinafter be called central if it is intended for all the cylinders in common, and local if it is intended for only a single cylinder.
In the pressure-controlled fuel injection system known from EP 0 711 914 A1, with the aid of a high-pressure pump, fuel is compressed to a first, high fuel pressure of approximately 1200 bar and stored in a first pressure reservoir. The fuel at high pressure is also fed into a second pressure reservoir, in which a second high fuel pressure of about 400 bar is maintained by regulating the fuel delivery to the second pressure reservoir by means of a 2/2-way valve. Via a central valve control unit and a central distributor device, either the lower or the higher fuel pressure is introduced into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can emerge from the nozzle opening.
In this known injection system, the lower fuel pressure cannot be metered optimally, for instance for the preinjection, because of line losses along the relatively long lead lines to the injectors.
From International Patent Disclosure WO98/09068, a stroke-controlled injection system is also known, in which again two pressure reservoirs for storing the two fuel pressures are provided. Once again, the metering of the applicable fuel pressure is effected via central valve units.
To attain improved metering of the lower fuel pressure, the injection method of the invention has definitive characteristics, and the injection system of the invention has the definitive characteristics set forth herein. Refinements according to the invention are recited hereinafter.
According to the invention, it is proposed that the lower fuel pressure be generated not centrally but rather locally for each injector, dissipatively via a diversion unit. Because of the short line between the local diversion unit and the nozzle chamber of the injector, line losses are reduced to a minimum. Because of the local generation of the lower pressure, no second pressure reservoir is needed. Further advantages are the good replicability of the preinjection and postinjection with the lower fuel pressure, as well as a reduced influence on the preinjection and postinjection of component tolerances.
Further advantages and advantageous refinements of the subject of the invention can be learned from the description, drawings and claims.
Various exemplary embodiments of fuel injection systems of the invention, in which the lower fuel pressure for each injector is generated individually and dissipatively, are shown schematically in the drawings and described in detail in the ensuing description.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawing.